The production of oxygen or oxygen enriched air by nitrogen adsorption in zeolites is a well developed technical field. Different types of zeolites exist and a number of them have been developed especially for the production of oxygen or oxygen enriched air. Naturally, there has also been suggested a number of ways to utilize the oxygen or oxygen enriched air which is produced. In WO 99/49964 there is for example described the use of nitrogen adsorbing zeolites in respiratory air devices or in air-conditioning units. Still, nitrogen adsorbing zeolites have a potential for new uses within new technical fields.
Moreover, although the production of oxygen or oxygen enriched air by nitrogen adsorbing zeolites is a well developed technical field, there is a potential for further development of this technique. The zeolite structures used today e.g. often exhibit a limited effectiveness due to decreased reaction (i.e. adsorption or desorption) rates, which in turn depends on excessive production or consumption of heat during the reactions. More precisely, the adsorption of nitrogen takes place during increase of pressure and increase of temperature. When the temperature becomes too high however, the rate of the adsorption reaction decreases. Moreover, the desorption of nitrogen normally takes place during decrease of pressure and decrease of temperature. When the temperature becomes too low however, the rate of the desorption reaction decreases. A reason for this being a problem is that zeolites exhibit a poor thermal conductivity, which means that the temperature within a zeolite structure quite fast will rise or decrease to a temperature at which the reaction rate is negatively effected.
Yet another problem is to accomplish an effective process utilising several zeolite units, i.e. how to make best use of the zeolite material, considering its adsorption properties and functionality when close to saturation, in a process which utilises at least three zeolite units consecutively, operatively connected to each other.
EP 0 343 799 teaches a process in which two or more sorbent units/beds are intermittently operated in an adsorption stage and a desorption stage, heat being transferred between the units/beds during operation. Likewise, U.S. Pat. No. 4,165,972 and EP 0 537 597 teach heating and cooling by use of heat exchanger means. EP 0 537 597 also teaches that in very large size air separation plants, several adsorbent beds may be connected for parallel flow in one processing bank, in which case all of the beds will go through the same processing sequence together and simultaneously. Hence, the plurality of beds are not serially interlinked to each other.